This invention relates to the field of electrochemical cells, and more particularly to electrochemical cells having very high anode-to-cathode interfacial surface area, and therefore, high rate discharge efficiency.
Electrochernical cells are commonly employed to supply voltage for electrically operated devices, and particularly for portable electrically operated devices. Popular alkaline cells of the generally cylindrical type are commercially available in industry standard sizes including D-, C-, AA-, AAA-, and AAAA- cells. There is an increasing demand for alkaline cells, particularly alkaline cells of the commonly commercially available sizes, which exhibit improved discharge efficiency at high discharge rates.
A frequently used configuration for high discharge rate batteries is a spiral wound electrode assembly, also known as a jelly-roll type assembly, in which a positive electrode, a negative electrode, and a separator sheet, are spirally wound to provide a high surface area between the electrodes, whereby a high discharge rate is achievable. The spiral wound construction requires that the electrodes be provided with a separator to avoid shorting. If conventional separators, such as paper or cellulose separators are used, typically, approximately 10% to 20% of the total volume of a AA size jelly-roll cell with a 110 square centimeter anode-to-cathode surface area is consumed by non-active separator material. The increased interfacial surface area results in increased high rate capacity. However, the reduction in active material volume causes reduced capacity at low rates of discharge.
Another disadvantage with conventional spiral wound cell constructions, is that the machines used for spirally winding two electrodes and a separator are relatively expensive to fabricate, operate and maintain. Accordingly, improved methods and cell constructions are desired.
U.S. Pat. No. 5,869,205, assigned to Eveready Battery Company, Inc., the assignee of this invention, discloses an electrochemical cell having multiple anode compartments to increase anode-to-cathode interfacial area. One embodiment includes a first electrode disposed in a container, in which the first electrode includes four cylindrically shaped cavities, with a second electrode disposed within each of the four cavities. A conventional separator is disposed within each of the four cavities. While the cell configuration described in U.S. Pat. No. 5,869,205 achieves a substantial improvement in high rate capacity, conventional separators are used. Accordingly, the improved discharge efficiency at high discharge rates, which is associated with an increase in anode-cathode interfacial surface area, is also accompanied by a proportional increase in separator area and separator volume. Therefore, improved discharge efficiency at high discharge rates is achieved, at least in part, by sacrificing total capacity. It would be desirable to achieve even greater improvements in discharge efficiency at high discharge rates, and preferably to achieve such improvements without sacrificing total capacity.
U.S. Pat. No. 3,156,585 discloses a hermetically sealed storage battery comprising a plurality of concentrically arranged ring-shaped electrodes, each of which is separated from an adjacent electrode by a conventional separator. Although the patent does not specifically mention improved discharge efficiency at high discharge rates, the battery construction shown would be expected to have an increased anode-cathode interfacial surface area, and would be expected to exhibit at least some improvement in discharge efficiency at high discharge rates. However, the battery structure is extremely complicated, and would be difficult to manufacture at a competitive price. Any improvement in discharge efficiency at high discharge rates would be accompanied by a significant increase in separator area and volume, and, therefore, a significant decrease in total capacity. It would be desirable to provide alkaline cells having increased anode-to-cathode interfacial area, and which are simpler in design, and, therefore, less expensive, and which preferably achieve improved discharge efficiency at high discharge rates without sacrificing total capacity.
U.S. Pat. No. 6,326,102 B1, issued Dec. 4, 2001 and commonly owned by the assignee of this invention, discloses a high rate electrochemical cell comprising a first electrode of a first polarity disposed in a container, a second electrode of a second polarity disposed on one side of the first electrode, a first current collector disposed in contact with the first electrode, and an outer electrochemically active layer having the second polarity and being disposed on another side of the first electrode. A separator is disposed between the first electrode and the second electrode and between the second electrode and the outer electrochemically active layer. The construction disclosed in U.S. application Ser. No. 09/198,802 has the advantage of achieving a substantial increase in anode-to-cathode interfacial surface area, and hence an improvement in discharge efficiency at high discharge rates, using a relatively simple design which can be produced at a competitive price. However, because the separator between the first and second electrode and between the second electrode and the outer electrochemically active layer is a conventional separator, i.e., a separator typically having a thickness of several mils, the improved discharge efficiency at high discharge rates is accompanied with an increase in separator volume, and, therefore, a decrease in total capacity.
The invention pertains to batteries having high anode-to-cathode interfacial surface area, and improved discharge efficiency at high discharge rates. The invention also provides methods for making batteries having high anode-to-cathode interfacial surface area, and improved discharge efficiency at high discharge rates.
A battery in accordance with this invention includes a housing and a first electrode. The first electrode includes a coating on surfaces of the first electrode, wherein the coating functions as a separator. The coated first electrode is disposed in the housing. A flowable material comprising a second electrode material is also disposed in the cell housing. The flowable material surrounds the coated surfaces of the first electrode .
A method of this invention involves the steps of providing a first electrode, forming on a surface of the first electrode a coating which functions as a separator, disposing the coated first electrode in a housing, and disposing a flowable material comprising a second electrode material in the housing, with the flowable material surrounding the coated surface of the first electrode.